This article discusses externalities resulting from the presence of transnational corporations (TNCs) in the host country and the foreign direct investment (FDI) they undertake. The study consists of three parts. The first part contains definitions and explains the concepts of externalities and spillover effects accompanying FDI. It also looks at the differences between these two concepts. The author points out that the host country does not automatically benefit from FDI undertaken on its territory. For that to happen, a number of activities must be undertaken by both domestic enterprises and economic policy makers aimed at creating appropriate conditions for the absorption of modern technology. The second part discusses the theoretical basis for spillover effects. The aim of the third part, meanwhile, is to examine issues related to pecuniary and technological externalities. In the case of pecuniary externalities, the question is raised of how transnational corporations generate such effects and what mechanisms they use. The two main channels through which these effects are passed have been identified, namely backward spillover and forward spillover links, and the results of empirical studies in this area have been reviewed in order to answer the question of which type of relationship between transnational corporations and domestic companies is more promising and produces positive results. The analysis of technological externalities focuses on the three main transmission channels: demonstration effects, movement of workers, and competition effects. The analysis concludes with a summary containing some recommendations for economic policy in stimulating and strengthening spillover effects in the host country.